Support escaping literal dots and special characters in domain names

Among others, this is needed for PTR records for DNS-based service
discovery (DNS-SD) that contain "human friendly" names. The
backslash-escaping allows literal dots in the name (escaped) to be
distinguished from label-separator dots (not escaped).
See https://tools.ietf.org/html/rfc6763#section-4.3

Author: clue

src/Protocol/BinaryDumper.php

@@ -175,6 +175,15 @@ private function domainNameToBinary($host)
             return "\0";
         }
 
-        return $this->textsToBinary(\explode('.', $host . '.'));
+        // break up domain name at each dot that is not preceeded by a backslash (escaped notation)
+        return $this->textsToBinary(
+            \array_map(
+                'stripcslashes',
+                \preg_split(
+                    '/(?<!\\\\)\./',
+                    $host . '.'
+                )
+            )
+        );
     }
 }

src/Protocol/Parser.php

@@ -270,7 +270,19 @@ private function readDomain($data, $consumed)
             return array(null, null);
         }
 
-        return array(implode('.', $labels), $consumed);
+        // use escaped notation for each label part, then join using dots
+        return array(
+            \implode(
+                '.',
+                \array_map(
+                    function ($label) {
+                        return \addcslashes($label, "\0..\40.\177");
+                    },
+                    $labels
+                )
+            ),
+            $consumed
+        );
     }
 
     private function readLabels($data, $consumed)

tests/Protocol/BinaryDumperTest.php

@@ -177,6 +177,47 @@ public function testToBinaryForResponseWithSOARecord()
         $this->assertSame($expected, $data);
     }
 
+    public function testToBinaryForResponseWithPTRRecordWithSpecialCharactersEscaped()
+    {
+        $data = "";
+        $data .= "72 62 01 00 00 01 00 01 00 00 00 00"; // header
+        $data .= "08 5f 70 72 69 6e 74 65 72 04 5f 74 63 70 06 64 6e 73 2d 73 64 03 6f 72 67 00"; // question: _printer._tcp.dns-sd.org
+        $data .= "00 0c 00 01";                         // question: type PTR, class IN
+        $data .= "08 5f 70 72 69 6e 74 65 72 04 5f 74 63 70 06 64 6e 73 2d 73 64 03 6f 72 67 00"; // answer: _printer._tcp.dns-sd.org
+        $data .= "00 0c 00 01";                         // answer: type PTR, class IN
+        $data .= "00 01 51 80";                         // answer: ttl 86400
+        $data .= "00 2f";                               // answer: rdlength 47
+        $data .= "14 33 72 64 2e 20 46 6c 6f 6f 72 20 43 6f 70 79 20 52 6f 6f 6d"; // answer: answer: rdata "3rd. Floor Copy Room" …
+        $data .= "08 5f 70 72 69 6e 74 65 72 04 5f 74 63 70 06 64 6e 73 2d 73 64 03 6f 72 67 00"; // answer: … "._printer._tcp.dns-sd.org"
+
+        $expected = $this->formatHexDump($data);
+
+        $response = new Message();
+        $response->id = 0x7262;
+        $response->rd = true;
+        $response->rcode = Message::RCODE_OK;
+
+        $response->questions[] = new Query(
+            '_printer._tcp.dns-sd.org',
+            Message::TYPE_PTR,
+            Message::CLASS_IN
+        );
+
+        $response->answers[] = new Record(
+            '_printer._tcp.dns-sd.org',
+            Message::TYPE_PTR,
+            Message::CLASS_IN,
+            86400,
+            '3rd\.\ Floor\ Copy\ Room._printer._tcp.dns-sd.org'
+        );
+
+        $dumper = new BinaryDumper();
+        $data = $dumper->toBinary($response);
+        $data = $this->convertBinaryToHexDump($data);
+
+        $this->assertSame($expected, $data);
+    }
+
     public function testToBinaryForResponseWithMultipleAnswerRecords()
     {
         $data = "";

tests/Protocol/ParserTest.php

@@ -629,6 +629,36 @@ public function testParsePTRResponse()
         $this->assertSame('google-public-dns-b.google.com', $response->answers[0]->data);
     }
 
+    public function testParsePTRResponseWithSpecialCharactersEscaped()
+    {
+        $data = "";
+        $data .= "5d d8 81 80 00 01 00 01 00 00 00 00";             // header
+        $data .= "08 5f 70 72 69 6e 74 65 72 04 5f 74 63 70 06 64 6e 73 2d 73 64 03 6f 72 67 00"; // question: _printer._tcp.dns-sd.org
+        $data .= "00 0c 00 01";                                     // question: type PTR, class IN
+        $data .= "c0 0c";                                           // answer: offset pointer to rdata
+        $data .= "00 0c 00 01";                                     // answer: type PTR, class IN
+        $data .= "00 01 51 7f";                                     // answer: ttl 86399
+        $data .= "00 17";                                           // answer: rdlength 23
+        $data .= "14 33 72 64 2e 20 46 6c 6f 6f 72 20 43 6f 70 79 20 52 6f 6f 6d"; // answer: rdata "3rd. Floor Copy Room" …
+        $data .= "c0 0c";                                           // answer: offset pointer to rdata
+
+        $data = $this->convertTcpDumpToBinary($data);
+
+        $response = $this->parser->parseMessage($data);
+
+        $this->assertCount(1, $response->questions);
+        $this->assertSame('_printer._tcp.dns-sd.org', $response->questions[0]->name);
+        $this->assertSame(Message::TYPE_PTR, $response->questions[0]->type);
+        $this->assertSame(Message::CLASS_IN, $response->questions[0]->class);
+
+        $this->assertCount(1, $response->answers);
+        $this->assertSame('_printer._tcp.dns-sd.org', $response->answers[0]->name);
+        $this->assertSame(Message::TYPE_PTR, $response->answers[0]->type);
+        $this->assertSame(Message::CLASS_IN, $response->answers[0]->class);
+        $this->assertSame(86399, $response->answers[0]->ttl);
+        $this->assertSame('3rd\.\ Floor\ Copy\ Room._printer._tcp.dns-sd.org', $response->answers[0]->data);
+    }
+
     /**
      * @expectedException InvalidArgumentException
      */